Cellular differentiation is being studied in the simple multicellular organism Volvox, with special emphasis on V. carteri f. nagariensis. Three main lines of investigation being followed are: (1) genetics and physiology of a mutant locus which lowers the inducibility response, the normal response to the sexual hormone being 100% when not in limiting quantities, (2) intercrossing between the Japanese and newly isolated Indian strains of V. carteri f. nagariensis, and (3) comparison of the sexual hormones in the V. carteri f. weismannia complex in which there is limited cross-inducibility.